Generally, the invention relates to a new process for the recovery of protein having improved solution clarity at acid pH from proteinaceous aqueous solutions. More particularly, the invention relates to a new process for the recovery of protein having improved solution clarity at acid pH from cheese whey and the use thereof in the fortification of acidic beverages, which require protein solubility and solution clarity at acid pH.
It is known that most food products can be nutritionally improved by protein fortification. Proteins heretofore useful for protein fortification include for example, soy protein, casein, and cheese whey proteins. Recently, it has become desirable to nutritionally improve acidic beverages by protein fortification. However, protein fortification of acidic beverages has been especially difficult, since proteins exhibit decreased solubility and increased solution turbidity at acid pH.
Recently, there has been particular interest in the use of proteins recovered from cheese whey for protein fortification of acidic beverages. This interest relates to the acid solubility of undenatured cheese whey proteins, which remain in solution at acid pH during the cheese making process.
In addition to protein solubility at acid pH, protein fortification of acidic beverages requires the maintenance of solution clarity at acid pH. Therefore, even though a particular protein exhibits adequate acid-solubility, the use thereof in acidic beverages is prohibited if the solution clarity at acid pH is unsatisfactory under the conditions of use.
Generally, it is known that protein can be recovered from proteinaceous aqueous solutions by the phosphate precipitation of protein from the proteinaceous aqueous solution and the recovered protein can be made acid-soluble by the subsequent removal of phosphate ions by conventional methods, e.g., anionic ion exchange, electrodialysis, and the like. Specifically, it is known that precipitation of protein can be effected from protenaceous aqueous solutions by metaphosphoric acid addition at acid pH. The precipitated protein can then be resolubilized by the disassociation of the protein metaphosphate complex by the addition of an alkali, and the removal of the alkali metaphosphate by precipitation or dialysis.
More specifically, the above described method is disclosed in U.S. Pat. No. 2,377,624 wherein protein is recovered in water soluble form from animal matter, as for example, whey, bovine serum and the like. The basic steps of this process comprise the addition of metaphosphoric acid or the equivalent amount of a water soluble metaphosphate, hexametaphosphate, or the like capable of yielding metaphosphoric acid; adjusting the pH within the range of 4.3 to 1.0, or preferably to about pH 3.0; separating the precipitated protein metaphosphate complex from the liquid; adding alkali to the precipitated protein metaphosphate complex to raise the pH to between about 6.0 and 12.0, preferably to about pH 9.0, to thereby disassociate the protein metaphosphate complex; and lastly the removal of metaphosphate ions by means such as dialysis, or metaphosphate precipitation.
More recently, U.S. Pat. No. 3,637,643 disclosed that the protein-phosphate precipitate can be more easily recovered by initially substantially reducing or removing the divalent metal cations present in the proteinaceous solution by ion exchange, or selective precipitation of divalent metal cations by the addition of trisodium phosphate to the proteinaceous solution. The patent also teaches that the protein recovered from the redispersed alkali solution is made acid-soluble if the phosphate ion concentration is substantially reduced. The protein thus obtained can be used in acidic beverages.
However, none of the known processes yield acid-soluble protein exhibiting solution clarity at acid pH and therefore are not suitable for use in the fortification of acidic beverages requiring solution clarity. It has been found that although the known processes provide an acid-soluble protein the protein produces turbid solutions at acid pH. These turbid acidic protein solutions are not satisfactory for the fortification of acidic beverages which require protein solubility and solution clarity at acid pH.